In today's process technologies for the production of integrated circuits, many components in and on a substrate are produced by applying specific process technologies. In recent developments, for enhancing component properties and/or process technologies, components are produced on a substrate by applying different process technologies and/or process materials, and are then transferred to the integrated circuit, this being performed as a so-called printing process or transfer print. For example, a component produced, for instance, on the basis of GaN, in the example in the form of a high-voltage transistor, is transferred to a CMOS environment in order to provide the underlying CMOS circuit with properties which cannot, or only with very great efforts, be obtained otherwise.
By transfer printing, semiconductor components can be released from a first semiconductor wafer and transferred to a second semiconductor wafer by use of a stamp and printed thereon.
US 2009/0294803 A1, DE 11 2011 101 135 T5 and U.S. Pat. No. 8,664,699 B2 describe methods of transfer printing, in which semiconductor components can be transferred from a first semiconductor wafer to a new substrate by use of a stamp made of elastomeric material. This second substrate may, for example, also be a second semiconductor wafer. The components to be transferred are initially masked and etched free at the sides. In this etching step, etching is performed around the component except for small (narrow) so-called breakable connection elements (tether).
In a next etching step, etching is performed beneath the component, wherein the component is mechanically retained by the said connection elements.
A part of the components is brought into conformal contact with the surface of the stamp and released from the first semiconductor wafer by adhesion to the stamp, which means that the connection elements are fractured in this procedure. Depending on the fracture behavior of the connection elements, residues of the fractured connection elements are still visible at the sides of the released component, also in the following state.
Then, the components adhering to the stamp are moved by the stamp and brought into conformal contact with the new substrate. There, they are fixed. Residues of the fractured connection elements are (still) visible at the sides of the fixed component.
Using this method, it is possible to transfer, per stamping procedure, a plurality of GaN transistors from a first semiconductor wafer to a second semiconductor wafer, wherein the semiconductor wafers may differ in type of material, crystal orientation, wafer diameter and wafer thickness. After transfer printing, for example, insulation layers as well as conductive layers can be deposited all over the wafer and then structured in further semiconductor-process processing steps. The processing on the basis of a complete semiconductor wafer enables a cost-effective manufacture due to the parallel processing of a plurality of circuits in the same processing step. For example, transferred GaN transistors with high mobility can be covered with an insulation layer, which layer is then structured with vias and wired to a metallization layer or metal layer.
U.S. Pat. No. 7,932,123 B2 describes methods, according to which the functional structures are made “printable” by a plurality of so-called “release layers”.
U.S. Pat. No. 7,943,491 B2 and US 2013/0069275 A1 describe a controlled method, in which the adhesion forces occurring between a component to be transferred and the transfer stamp are changed by means of the separation rate in order to temporarily attach the components to be transferred to the stamp, and to then finally fix them to the receiving substrate. In the case of a fast separation, high adhesion forces are created so that the components are temporarily attached to the stamp and released from the donor substrate, wherein the components can be released from the stamp by use of low separation rates and thus low adhesion forces.
U.S. Pat. No. 7,799,699 B2 describes etching free AlGaN/GaN heterostructure components on (111) silicon. By suitable masking and vertical plasma etching (inductively coupled plasma), exposed, i.e. unmasked trenches are etched next to the component. In the horizontal direction, the components are etched free by etching the silicon substrate beneath the component with tetramethylammonium hydroxide (THAH). Mechanical fixing is performed in the horizontal direction by suitable interruptions of the trenches, i.e. by material bridges which are not etched away.
WO 2005/076679 describes a target substrate for a method for transfer printing which is also made of semiconductor materials, wherein nanotubes are applied to the substrate. Electrodes on the substrate serve the purpose of electrically contacting and mechanical attachment and orientation, respectively.
U.S. Pat. No. 6,332,561 B1 describes a substrate, in which soldering points are required for attaching a semiconductor component and an integrated circuit, respectively, on the substrate.
The above-described prior art provides promising approaches for transferring components of a first type to a substrate, on which components of a second type have been produced or are produced. However, for ensuring the required functionality of the transferred components on the receiving substrate, a suitable electrical, mechanical and thermal connection to the receiving substrate is required.